Wear resistant alloy steel



ice

WEAR RESISTANT ALLOY STEEL Peter Payson and David I. Dilworth, Jr., Pittsburgh, Pa.,

assignors to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New. Jersey N Drawing. Application January 16-, 1957 Serial No. 634,408

6 Claims. (Cl. 75-126) This invention pertains to a high carbon alloy steel containing as essential constituents chromium, vanadium and molybdenum in proportions such as to impart wear resistance and high hardenability to relatively thick sections upon air cooling from the austenitizing temperature range. For improving forgeability the steel of the invention also preferably contains a small amount of tungsten.

The object of this invention is to provide a forgeable wear resistant steel to be used for blanking dies, drawing dies, thread rolling dies, mandrels, burnishing tools, gauges, brick mold liners, sand slinger liners, and the like. A further object is to provide a wear resistant steel of high hardenability so that fairly large sections can be hardened adequately by an air cool from a suitable austenitizing temperature.

The steel of this invention is based on the use of high carbon from about 1.65 to 2.75% along with fairly high vanadium, from about 2.0 to 5.0%, to provide a large quantity of hard, abrasion-resistant residual carbides in the microstructure of the hardened steel. To provide adequate hardenability in the steel so that sections as large as three inches, and even four inches, thick, may be hardened to a minimum of Rockwell C 62 on air cooling from a suitable austenitizing temperature, say 1800 F., chromium is used from more than up to about 6.5%, and molybdenum from about 1.75 to 5.0%, along with the carbon and vanadium mentioned above. For improving forgeability tungsten is preferably added in amount up to about 1.5%, the lowest effective limit being about 0.25%.

The broad and preferred ranges of these elements in the steel of this invention are as follows:

The manganese in the steel i usually held within the range 0.20 to 1.00%; and silicon generally from 0.20 to 1.50%.

Since the steel as annealed is ordinarily difiicult to machine because of the large quantities of fairly massive alloy carbides in the structure, we may use up to 0.50% sulfur as an addition to the steel, the sulfur being added either as the element itself, or in the form of a compound with other elements which enter the steel during the melting. The balance of the steel is substantially or all iron.

To evaluate the hardening of steels in fairly heavy sections on air cooling from suitable austenitizing temperatures, it is not necessary to make up bars of the sizes in question. Such a procedure would indeed be very expensive in a development program because it would be necessary to melt heats of at least 150 lbs. of each analysis so that an ingot would be produced of sufiicient Patented Jan. 6, 1 959 size to make satisfactory bars about four inches thick. Generally, in a development program much smaller beats are made, of the order of 15 to 30 lbs, and-bars are forged from these ingots to about five-eighths to one inch in section. Tostudy the hardening of a large section when only small sections are available, it is merely necessary to heat the small sections to a suitable austeniti'zing temperature and then to cool them according to the temperature-time relationships known to exist for various size bars cooled in various quenchan'ts. Such cooling schedules are available in the literature, for example, in the classic paper by H. J. French, A Study of the Quenching of Steels, Trans. ASST, vol. 17, 1930. Cooling schedules for practically any size bar can be followed with small pieces by moving them through a series of lead .or salt baths maintained at an appropriate series of temperatures, if a thermocouple is attached to the test piece and connected to a suitable potentiometer. The. movement of the test piece from one temperature level to the next is governed by the published schedule for the particular size bar the cooling of which is being simulated. Admittedly the published cooling schedules for large bars may be applied only to steels in which no transformation other than the martensite reaction occurs because it is known that the exothermic reaction accompanying high temperature transformations would appreciably alter the cooling schedule.

To show the hardening responses of the steel of this invention, and to show also the efiects of variations in some of the elements used in the steel, cooling schedules for three inch and four inch round bars cooling in air from 1800 F. were followed. Samples of commercial air hardening die steels were run as controls along with samples of the steel of this invention. Pertinent composition and hardness data are given in Table I below:

Table 1 Rockwell 0 hardness-Samples cooled from 1,800 Bar 0 0r V Mo I at rate of air cooled 3 in. rd. 4 in. rd

NOTE. Bars 8828, 8829, and 3350 represent commercial air hardentug die steels. Bars 3688 and 3238 are steels of this invention.

It is evident from these data that in the high carbon steel of this invention both increasing vanadium and increasing molybdenum are eflective in increasing hardenability of the steel, and when both vanadium and molybden'um are above the low limits indicated in our broad range, as in Bars 3688 and 3238, the steel hardens to a minimum of Rockwell C 62 when cooled from 1800 F. in air in sizes up to and including four inch round.

The steel of this invention is quite resistant to softening at temperatures up to 900 F. and maintains a hardness of C 60 or higher when tempered cumulatively for two hours at temperatures from 500 to 900 F.

Although the steel of this invention is forgeable, we may also use it as castings if design and service of, the part make casting a more economical procedure.

This application is a continuation-in-part of our copending application Serial No. 450,556, filed August 17, 1954, now abandoned.

. 3 I What is claimed is:

l 1. A forgeable and wear resistant alloy steel containing about: 1.65 to 2.75% carbon, from more than 5% to 6.5% chromium, 2 to 5% vanadium, 1.75% to 5% molybdenum, up to 1% manganese, up to 1.5 silicon, up to 1.5% tungsten, up to 0.5% sulfur, and the balance substantially iron, characterized in being hardenable to a minimum of C 62 Rockwell in sections up to about four inches round, on air cooling from about 1800 F.

2. An alloy steel consisting of about: 1.65 to 2.75% carbon, from more than 5% to 6.5% chromium, 2 to 5% vanadium, 1.75 to 5% molybdenum, up to 1% manganese, up to 1.5% silicon, up to 0.5 sulfur, up to 1.5 tungsten, and the balance iron.

3. A forgeable and wear resistant alloy steel containing about: 2.1 to 2.5% carbon, 5.25 to 5.75% chromium, 3.25 to 4.25% vanadium, 2.0 to 3.5% molybdenum, 0.25

to 1% tungsten, 0.2 to 1% manganese, 0.2 to 1.5 silicon, up to 0.5% sulfur, and the balance substantially iron,

characterized in being hardenable to a minimum of C 62 Rockwell in sections up to about four inches round, on air cooling from about 1800 F.

4. An alloy steel consisting of about: 2.1 to 2.5% carbon, 5.25 to 6% chromium, 3.25 to 4.25% vanadium, 2.0 to 3.5% molybdenum, 0.25 to 1% tungsten, 0.2 to 1% manganese, 0.2 to 1.5% silicon, up to 0.5% sulfur, and the balance iron.

5. A wear resisting article made of an alloy steel according to claim 1.

6. A wear resisting article made of an alloy steel according to claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 2,174,281 Gill Sept. 26, 1939 2,278,315 Houdremont et al Mar. 31, 1942 2,575,219 Giles Nov. 13, 1951 

1. A FORGEABLE AND WEAR RESISTANT ALLOY STEEL CONTAINING ABOUT: 1.65 TO 2.75% CARBON, FROM MORE THAN 5% TO 6.5% CHROMIUM, 2 TO 5% VANADIUM, 1.75% TO 5% MOLYBDENUM, UP TO 1% MANGANESE, UP TO 1.5% SILICON, UP TO 1.5% TUNGSTEN, UP TO 0.5% SULFUR, AND THE BALANCE SUBSTANTIALLY IRON, CHARACTERIZED IN BEING HARDENABLE TO A MINIMUM OF C 62 ROCKWELL IN SECTIONS UP TO ABOUT FOUR INCHES ROUND, ON AIR COOLING FROM ABOUT 1800* F. 